1. Field of Invention
The invention relates generally to a semiconductor device that exhibits extraordinary piezoconductance, or increased conductance under pressure/strain, and to a sensor using such a semiconductor device.
2. Description of Related Art
Inhomogeneous semiconductors have previously been shown to exhibit extraordinary magnetoresistance (EMR), as discussed in S. A. Solin et al., “Enhanced Room-Temperature Geometric Magnetoresistance in inhomogeneous Narrow-Gap Semiconductors”, Science, vol. 289, pp. 1530–1532, Sep. 1, 2000. This effect derives from magnetic field induced changes in the conductive boundary conditions at an internal metal (shunt)/semiconductor interface within the device. Fabrication of galvanomagnetically equivalent externally shunted planar structures (EMR plates), discussed in T. Zhou et al., “Extraordinary magnetoresistance in externally shunted van der Pauw plates,” Appl. Phys. Lett. Vol. 78, pp. 667–669, Jan. 29, 2001, is far cheaper than the initially studied internally shunted circular geometry, and when scaled to nanoscopic size, as discussed in S. A. Solin et al., “Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording,” Appl. Phys. Lett., vol. 80, no. 21, pp. 4012–4014, May 27, 2002, these devices show great promise as nonmagnetic read head sensors for magnetic storage media. Macroscopic EMR plates also have a number of large volume applications in the automotive and other industries such as position sensing of rotating parts.
Here we disclose a new effect observed in macroscopic EMR plate structures that were originally designed as test devices for the EMR effect. The new effect consists of a large increase in the conductance of the EMR plates in the presence of an applied strain. Like EMR, the origin of the effect lies in changes to the conductive boundary conditions at the metal/semiconductor interface under an external perturbation (in this case strain) as will be shown using a finite element analysis of the EMR plates. This effect, which we dub extraordinary piezoconductance (EPC), produces enhancements in the piezoconductance of almost an order of magnitude compared with the response of homogeneous semiconducting material.